Electrostatic sampler and method

ABSTRACT

The present invention is an electrostatic collector for low cost, high throughput, high efficiency sampling and concentration of bioaerosols. The device is small enough to be portable and can be contained within or placed on the wall of a typical office or hospital building. The collector comprises one or more collector modules, each having an ionizing electrode, a conical outer electrode, a wet collection electrode, and a liquid collection system. Airflow through a collector module may be partially blocked to enhance the collection of smaller particles and the collection electrode may comprise multiple, programmable electrodes to focus particle deposition onto a smaller area. Particles are collected into a small volume of liquid to facilitate subsequent analysis by an attached analyzer or at a remote site.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Statement of Government Rights

The U.S. Government may have certain rights in this invention pursuantto HSARPA SBIR Contract NBCHC040110 awarded by the Department ofHomeland Security.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

INCORPORATED-BY-REFERENCE OF MATERIALS ON A CD

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to electrostatic samplers and methodsused to collect aerosolized particulates. The particulates are collectedon a dry collection surface or in a buffer solution or other liquid tofacilitate subsequent processing and analysis. In particular, thisinvention provides a miniaturized electrostatic sampler designed forhigh efficiency and low energy (cost) collection of airborneparticulates. The airflow through the sampler, electric fields, andcollector geometry were obtained using physics-based computationaloptimization methods to maximize capture efficiency and selectivity fora target particle size while minimizing power consumption and devicefootprint.

2. Description of Related Art

The detection and analysis of aerosolized biological agents such asbacteria, bacterial, mold, and fungal spores, and viruses is desirablein a wide variety of settings including civilian environs such ashospitals, office buildings, and sports arenas, as well as militaryenvironments such as the battlefield, observation posts, and militaryhousing. The ability to detect airborne particles such as bacteria andbacterial spores is critical to areas where accidental or deliberaterelease of harmful biological agents is suspected and can greatly helprisk assessment and management, decontamination/neutralization andtherapeutic efforts. Rapid detection of airborne pathogens can controlthe spread of bacterial infections in hospitals, schools, and animalfacilities, for example.

In recent years, increasing concern has been expressed over thedevelopment of fast, accurate and robust countermeasures against theemergent threat of bioterrorism. A comprehensive review of biodetectiontechnologies is provided in the following reference: NATIONAL RESEARCHCOUNCIL OF THE NATIONAL ACADEMIES (2005) “Sensor Systems for BiologicalAgent Attacks: Protecting Buildings and Military Bases” Committee ofMaterials and Manufacturing Processes for Advanced Sensors, Board onManufacturing and Engineering Design, Division on Engineering andPhysical Sciences, The National Academies Press, Washington, D.C.Typically, the process of biodetection can be broadly sub-divided intothe following steps: (1) sampling, where the airborne particles arecaptured into a suitable solid, liquid or gaseous matrix, (2) samplepreparation, where the aforementioned matrix is processed to render thetarget entities in a format aligned with the downstream detector, and(3) sensing, where the target moieties in the sample are identified.

Reviews of bioaerosol sampling strategies are provided in the followingreferences: National Institute of Justice (NIJ) Guide 101-00 (2001) “AnIntroduction to Biological Agent Detection Equipment for Emergency FirstResponders” US Department of Justice, Washington, D.C.; and HENNINGSONet al. (1994) “Evaluation of Microbiological Aerosol Samplers: A Review”Journal of Aerosol Science 25(8):1459-1492. Existing bioagent samplingtechnologies are largely based on (a) interception (such as filters),(b) inertial separation mechanisms (such as impingers, impactors,cyclones and centrifuges) or (c) electrostatic principles. Interceptionbased aerosol samplers are a primarily intended for air purification andsuffer from high costs of maintenance, difficulties in interfacing withanalysis modalities and pre-determined cut-off size for sampling.Inertial separation mechanisms suffer from the disadvantages of highcost of operation, high power consumption, low collection efficienciesof viable microorganisms, and high cost of manufacturing/machining.Electrostatic precipitators, as opposed to samplers/collectors, arecommonly used as air purifiers designed to filter air and not to captureairborne particulates on a substrate or matrix for analysis. Existingelectrostatic samplers are too large for portable applications and usevoltages that kill or damage many organisms, thus preventing orcomplicating organism detection and identification.

Recently, the use of electrostatic samplers for collection of airbornemicroorganisms was demonstrated by the following references: MAINELIS etal. (2002) “Design and Collection Efficiency of a New ElectrostaticPrecipitator for Bioaerosol Collection” Aerosol Science and Technology36:1073-1085; and MAINELIS et al. (2002) “Collection of AirborneMicroorganisms by a New Electrostatic Precipitator, Journal of AerosolScience 33:1417-1432, which are incorporated by reference in theirentirety. A simple design comprising a parallel plate electrodeconfiguration was used for developing the proof-of-concept in thesestudies. Physical collection efficiencies of >90% and biologicalcollection efficiencies of >70% were demonstrated for air flow rates upto 8 L/min. Electrostatic samplers use an externally applied voltage tocharge particulates in the air and deposit them on a collection surface.The collection surface can be an electrode with a dry surface or anelectrode covered with a stationary or moving liquid. Electrostaticcollectors (samplers) that deposit particles in a liquid medium can beused to concentrate samples from the air and deliver them to fluid-basedbiological assay modules such as microfluidic chips for analysis. Thisformat is particularly useful for detecting or identifying biologicalagents such as bacteria, viruses, and bacterial, mold, and fungalspores, for example.

U.S. Patent Publication 2004/0083790 (CARLSON et al.) describes aportable liquid collection electrostatic precipitator. The devicecomprises: a hollow, vertical, tubular collection electrode; a groundplate adjacent to the collection electrode; a reservoir for a liquid, apump for pumping the liquid, and an ionization section to ionizeanalytes in the air. Particles in the air are ionized, attracted to thecollection electrode, and precipitated in the liquid. The devicedescribed by CARLSON et al. uses a high voltage collection electrode of6,000-8,000 volts to attract charged particles, an airflow rate of 300L/min, and can be powered by a 12-volt automobile battery. High voltagessuch as those applied to the Carlson et al. collection electrode cankill many organisms and thereby prevent or make more difficult theirdetection and/or identification. In addition, the high voltage appliedat the collection electrode, which is normally bathed in aqueous liquid,poses a significant safety hazard. The CARLSON et al. sampler does notdisclose the collection of small diameter particles with highefficiencies or designs capable of miniaturization while maintaininghigh collection efficiencies.

There remains an unmet need in the art for a miniaturized, portableelectrostatic air sampler that can collect particles, including viableairborne viruses and bacterial spores, with high efficiency.

The present inventors have applied physics-based computational fluiddynamics (CFD) analysis to design novel, miniaturized electrostaticsamplers that occupy less space, consume less power, capture particleswith higher efficiency, and have greater operational flexibility thanexisting electrostatic samplers/collectors. Several innovative conceptsfor high throughput sampling were identified and evaluated using coupledairflow, particle transport and electric field simulations. Theoptimized samplers have predicted collection efficiencies of >90% at<5,000V and 60 L/min, even for 1 μm particles. Clustering of collectorsin an electrostatic sampler array can easily achieve airflow rates of300-1000 L/min and higher. A high voltage outer electrode allows the useof a grounded collection electrode to maintain the viability ofcollected cells and spores. The outer and/or collection electrode may besegmented to form programmable electrode array(s) to enhance efficiencyand to reduce the area onto which particles are deposited. Testing of aprototype electrostatic sampler design has verified the performancepredicted by CFD simulations.

BRIEF SUMMARY OF THE INVENTION

The present invention provides various embodiments of a miniaturizedelectrostatic air sampler comprising at least one electrostaticcollector module (ECM) for depositing airborne particulates such asbioagents, dust particles, and aerosolized chemicals, onto a drysubstrate or into a small volume of liquid collection medium. Theelectrostatic air sampler operates with high particle captureefficiencies using outer electrode voltages of less than 5,000 volts,more preferably, less than 2000 volts, and most preferably, less than1000 volts, and consumes less than 100 Watts for the device and lessthan 10 Watts for each ECM. The miniaturized sampler is capable ofcollecting viable, aerosolized organisms from the air or other gasses tofacilitate the analysis, identification, and quantification of theorganisms. The miniaturized sampler can operate on battery power forportablility and maintains at least 90% collection efficiency forparticles having diameters of 1-10 μm while operating at air flow ratesof between about 60 L/min to 1000 L/min. The miniaturized electrostaticsampler may be coupled to at least one analyzer for detecting oridentifying at least one specific bioagent, and may be equipped totransmit information related to the presence, absence, and/orconcentration of one or more bioagents in the collected sample and/orthe sampled air to a local or remote location.

Important findings during the design of the present miniaturized airsampler include: the superior performance of tapered, especiallyconically shaped ionizing electrodes, the ability to enhance smallparticle capture by selectively blocking airflow through portions of theECM, and the ability to selectively focus particle deposition ontoregions of the collecting electrode by using a variable voltage outerelectrode array.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a cut away view one prototype electrostatic samplercomprising one ECM with a wet collection electrode.

FIG. 2 illustrates one embodiment of the electrostatic sampler used forbiohazard detection.

FIG. 3A depicts a first embodiment of an ECM.

FIG. 3B shows the simulated size-based collection efficiency for the ECMembodiment shown in FIG. 3A.

FIG. 4A shows a second embodiment of an ECM.

FIG. 4B shows the simulated size-based collection efficiency for the ECMembodiment shown in FIG. 4A.

FIG. 5 compares the simulated size-based collection efficiencies offirst and second embodiments of an ECM for small particles.

FIG. 6A-D illustrate the effects of blocking flow on particle capture.

FIG. 7A-D illustrate the effects of blocking flow on particletrajectories.

FIGS. 8A and B show simulated overall and effective collectionefficiencies

FIGS. 9A and B an arrayed arrangement of partially blocked ECMs

FIGS. 10A and B illustrate one embodiment in which performanceimprovements can be achieved by applying a programmed variable voltageto the outer electrode instead of a constant voltage.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one prototype electrostatic sampler comprising one ECM 10with a wet collection electrode 2. A housing 11 contains ECM 10, liquidinlet 6, liquid outlet 7, and reservoir 8. The position of theionization electrode 5 relative to the ECM 10 is indicated. During wetelectrode operation, the sampler is vertical and a pump (not shown)pumps liquid into liquid inlet 6 and into the hollow cavity 9 of thecollection electrode 2. The hollow cavity 9 fills and liquid flows overthe lip 12, down the sides of the collection electrode 2, and into thereservoir 8. Fluid from the reservoir may be recirculated into liquidinlet 6 or transferred, for example, to an analytical device. Air entersthe ECM through air inlet 3, travels through the ECM between the outerelectrode 1 and collection electrode 2, and exits through air outlet 4.Airborne particles are charged by the ionization electrode 5 and aredriven into the liquid covering collection electrode 2 by a high voltageapplied to outer electrode 1, which has the same charge as that imposedon the particles. The collection electrode 2 is grounded and has acharge opposite that of the particles and outer electrode.

The ionization electrode and outer electrode are energized by a highvoltage potential provided by an electrical power supply. The powersupply may be, for example, standard 110 or 220 AC or one or more DCbatteries for portable operation. High voltages may be generated by wellknown means such as transformers or voltage amplifiers.

For some applications, it may be advantageous to include a chargeneutralization section upstream of the location of the ionizationelectrode 5. In most cases, an electrostatic sampler will operate usingan ionizing electrode that imparts a negative charge on airborneparticles combined with a positively charged collection electrode. Thisis done because most biological particles carry or are easily caused tocarry a negative charge. Some naturally occurring or manufacturedbiological aerosols carry a positive charge and do not maintain negativecharges very well. Pretreatment with a charge neutralizer removespositive charges from these particles and makes it easier to imparting anegative charge on them. This tandem arrangement of charge neutralizerfollowed by ionization electrode can be used, for example, to sample forparticles that naturally carry negative charges and those that carrypositive charges. To specifically sample for particles carrying apositive charge, one would use an ionization electrode that imparts apositive charge on particles in combination with a negatively chargedcollection electrode.

FIG. 2 illustrates one embodiment of the electrostatic sampler used forbiohazard detection. Shown are: electronics for power supply modulation21, a modular electrostatic sampling unit 22 comprising more than oneECM, a detachable well for collected sample analysis 23, an outlet to adetection platform 24, control panel and digital readout display 25, anindicator alarm 26, and active air intake 27.

FIG. 3A shows one embodiment of an ECM. The ECM comprises a conical,high voltage outer electrode 1, forming at least a part of the outerwall of airflow channel 5 and a cylindrical, grounded, collectingelectrode 2. This particular embodiment shows the collecting electrode 2having a lighter shading than the upstream segment of the interiorsurface of the airflow chamber. In other embodiments, the collectionelectrode may comprise more or less of the interior surface of theairflow chamber. An ionization electrode upstream of and near the airinlet 3 is not shown. Air enters the ECM through inlet 3 and exitsthrough outlet 4 of lesser diameter than inlet 3. Airflow can be forced,for example, by a fan, blower, or pressure differential or it can bepassive and depend on the prevailing air currents around the sampler.

The shape of the outer electrode is most preferably a continuouslynarrowing conical shape but may have any continuously tapering shapefrom the air inlet to the air outlet. The outer electrode may also havea conical shape combined with cylindrical extensions at either end. Theouter electrode may comprise a single, continuous segment of conductingmaterial or a segmented series of electrodes that are insulated from oneanother to facilitate the programmed application of voltages toindependent electrode segments. The outer electrode may comprise aportion of or all of the outer surface of the airflow channel 5. Theouter electrode may be made of a conducting metal such as copper, gold,or platinum, a conducting polymer, or a nonconducting material coatedwith a conducing layer.

Ionized particles are directed toward the collection electrode by anelectric field generated at the outer electrode. The collectionelectrode may be a solid or hollow cylinder of conducting material ornonconducting material coated with a conducting layer. Particlesdeposited on the collection electrode may be recovered in a variety ofways. It the collection electrode is dry, deposited particles may betransferred to a material used to wipe the electrode or transferred intoa container by scraping, blowing, or other means. If the electrode iswet, liquid may be dispensed over the surface of the electrode in acontinuous or discontinuous fashion. Liquid may be recirculated over theelectrode and periodically transported to an analysis unit orcontinuously or discontinuously flow over the collection electrode andinto an analysis unit.

For wet electrode operation, the ECM further comprises a pump and liquidreservoir, which provide a periodic or constant film of collectionliquid flowing over the surface of the grounded collection electrode.During wet electrode operation, the electrode should be evenly coveredby a thin film of liquid, which may be water, an aqueous buffer, anorganic solvent, an oil, or any other suitable fluid that can form athin, flowing layer on the collection electrode. The collectionelectrode may be coated with a material to facilitate even spreading ofthe liquid and/or the liquid may comprise a surfactant to facilitateeven spreading. The wet collection electrode is normally a verticalhollow cylinder that fills at the bottom with fluid from a pump, withliquid running over the top lip of the cylinder, down the outer walls,and into a reservoir that feeds back into the pump. The top of thecollection electrode cylinder may be partially covered but may notinterfere with fluid flow over the lip to the outside walls. Thecollection electrode and ECM need not be vertical during wet operationin microgravity conditions or if a continuous, thin layer of liquid canbe maintained on the collection electrode and the liquid can be returnedto the reservoir.

CFD simulations of airflow through the ECM show that, compared to acylindrical shape, the conical shape of the outer electrode increasesflow stability, particularly when airflow around the air inlet 3 ischaotic, as would be the case for a sampler used outdoors with variablewinds. The conical design also directs airflow toward the collectionelectrode, increasing collection efficiency. The angle of the conicalelectrode is preferably between 1⁰ and 4⁰ to optimize airflow stabilitywithout decreasing efficiency caused by increased air velocity at thecollection electrode. The ECM can be modified to optimize the collectionefficiency for certain particle sizes and densities. The air inlet andoutlet may be partially blocked to enhance the efficiency for smallparticle collection, for example. The outer electrode may also besegmented to allow variable voltage application along the outerelectrode to direct selected particles toward specified areas of thecollection electrode.

FIG. 3B shows the size-based, CFD simulated collection efficiencies ofthe ECM shown in FIG. 3A. Larger particles are collected with higherefficiency at lower outer electrode voltages, while smaller particlesare collected with higher efficiency at higher voltages. The collectionefficiencies predicted by CFD simulations have been experimentallyvalidated using an actual corresponding prototype ECM with airborneparticulates including polymer beads and sub-micrometer sized saltparticles.

FIG. 4A shows a second embodiment of an ECM that was redesigned tooptimize small particle collection using CFD simulations. The collectingelectrode 2 of this embodiment is shown in a lighter shade than theupstream portion of the inner wall of the airflow chamber. Thesize-based CFD simulated collection efficiencies for small particles ofthe second embodiment ECM are shown in FIG. 4B. The collectionefficiencies for smaller particles are improved over those for the ECMshown in FIG. 3A. FIG. 5 compares the small particle collectionefficiencies of the ECMs shown in FIG. 3A (open circles and triangles)and FIG. 4A (shaded circles and triangles). The collection efficienciesfor 1 μm and 3 μm particles are virtually 100% below applied outerelectrode potentials of 5,000 volts for the second ECM. The CFDsimulations have been supported by the results of experiments using twocorresponding prototype ECMs with airborne particulates includingpolymer beads and sub-micrometer sized salt particles.

In some embodiments of the invention, it may be desirable to alter thepattern of airflow through one or more ECMs. For example, one may placevanes that are slanted or otherwise shaped to induce tangential, spiral,laminar airflow in the ECM. Such flow increases particle residence timein the ECM and prolonging the time during which charged particles areexposed to the electric field driving them toward the collectionelectrode. In some cases it may be advantageous to partially block theair inlet and outlet of one or more ECMs. For example, for manifoldsamplers that comprise multiple ECMs in close proximity, it may beadvantageous to partially block inlet and outlet ends to prevent theseparation of air and liquid sample streams. The blocked areas at inletand outlet ends would be maintained anti-symmetric to the centerline toavoid “short-circuiting” of particles in the chamber. Coupledmultiphysics simulations were carried out to evaluate a modular designcomprising 5 ECMs arranged in parallel and in a pentagonal arrangement.FIG. 6A-D shows sample simulation results for both 3D and projectedparticle trajectories. The effective inlet area is shown by dark grayfor 0, 25%, 50% and 75% blockage.

Partially blocking the air inlet and outlet introduces cross-flowpatterns in the airflow chamber and enhances the collection of smallerparticles. FIG. 6A-D shows the simulated distributions of capturedparticles on the collection electrode for different levels of airflowblockage. Particle capture is not symmetrically distributed on thecollection electrode because of cross-flow. More particles are capturedon the “windward” side of the inner electrode than the “leeward” side.Partially blocked ECMs may be used to enhance small particle collectionwhile reducing large particle collection or to focus collection on aparticular area of the collection electrode. Reducing the area ofdeposition in the collection electrode may, for example, allow the useof smaller volumes of liquid for particle collection or, in the case ofdry collection electrodes, may allow a higher concentration of depositedparticles for collection by other means.

FIG. 7A-D shows the particle trajectories for different levels ofairflow blockage. The effective blockage at the inlet is shown in whitefor 0, 25%, 50% and 75% blockage. Since part of the outlet is blocked,higher particle velocity and cross-flows cause some particles to be lostat the exit. The simulated overall collection efficiencies are shown inFIG. 8. The overall collection efficiency contains particles captured onthe inner electrode as well as those on the end wall. An increase inblockage (decreasing S_(in)/S₀) leads to an increase in the collectionefficiency of small particles and a loss of larger particles at theoutlet.

Partially blocked ECMs may also be useful when combining several ECMsinto one sampler device. FIG. 9A-B show an array of four partiallyblocked ECMs 31, 32, 33 and 34 arranged in a circular fashion. Due tothe annular path of the air stream, it is advantageous to employpartially blocked ECMs in arrayed configurations. The inlet airflow path36 is shown in FIG. 9A-B along with air exit stream 37. Partial blockingof the proximal (inlet) and distal (outlet) ends of the ECM allows therealization of a simplified manifold such as a single manifold 35located near the axis of a circular array of ECMs. For wet electrodecollection, the simplification of airflow manifold design can bepropagated to the distal end and harnessed for a centralized collectionbuffer manifold 39 fed by the liquid stream 38 from individual ECMs. Onesampler device may have any number of identical or different ECMscombined in parallel and/or in series, depending on the desiredapplication. For example, parallel configurations allow for increasedairflow while ECMs in series may allow for sequential optimized samplingfor different airborne species. Other examples of advantages provided byECM arrays include simultaneous optimized sampling for differentairborne particles and redundancy for internal controls and reduction offalse positive and false negative results.

In another embodiment of the invention, it may be desirable to segmentthe outer, conical electrode so that the potential is applied in aprogrammed fashion as opposed to a constant, uniform potential. Thisleads to improved collection efficiency and a more focused collection ofparticles as shown in FIGS. 10A and B.

EXAMPLE

Two prototype electrostatic samplers representing two embodiments of theinvention were fabricated and tested. The design and performancespecifications based on experiments using airborne polystyrene beads aredisplayed in Table 1 for one of the samplers.

TABLE 1 Specifications for a One Embodiment of an Electrostatic SamplerDesign Specifications Performance Specifications Electrode Shape ConicAir Flow Rate 60 L/min Chamber Length 50-100 mm Pressure Drop <1″ ofwater Electrode Length 25-50 mm Collection Efficiency >90% (1-10 μm)Electrode Diameter 15 mm Liquid Collection Volume 10 ml Inlet Diameter28 mm Applied Voltage 2000-5000 V Outlet Diameter 22 mm Size & Weight 1ft³, ~2 lb

It will be appreciated by those having ordinary skill in the art thatthe examples and preferred embodiments described herein are illustrativeand that the invention may be modified and practiced a variety of wayswithout departing from the spirit or scope of the invention.Combinations of sampler, ECM, outer electrode, collection electrode, airinlet and air outlet dimensions, outer and collection electrode shapes,programmed application of voltages to segmented outer electrodes, andcombinations of ECMs into samplers may be adapted for particularsampling needs without departing from the present invention.

1. An electrostatic air sampling device comprising: an electrostaticcollection module comprising: an airflow chamber comprising an airpassage having an air inlet and an air outlet; a means of drawing airinto the air inlet, through the airflow chamber, and out through the airoutlet; an ionization electrode located near the air inlet, theionization electrode being capable of ionizing airborne particles; aconical outer electrode forming at least a part of the outer wall of theairflow chamber and having a larger diameter toward the air inlet and asmaller diameter toward the air outlet; a cylindrical, collectionelectrode, the exterior surface of which forms at least a part of theinner wall of the airflow chamber and upon which airborne particles arecollected; and a power source operatively connected to the electrostaticcollection module, said power source providing power to energize theionization and outer electrodes.
 2. The electrostatic air samplingdevice of claim 1, wherein the total length of the electrostaticcollection module is less than 25 cm and the total width of theelectrostatic collection module is less than 10 cm.
 3. The electrostaticair sampling device of claim 1, wherein the air inlet and air outlet ofthe airflow chamber are partially blocked.
 4. The electrostatic airsampling device of claim 1, wherein the air inlet of the airflow chambercomprises one or more vanes that cause tangential, spiral, laminarairflow in the airflow chamber.
 5. The electrostatic air sampling deviceof claim 1, wherein the conical, outer electrode comprises a series ofelectrode segments.
 6. The electrostatic air sampling device of claim 1,wherein the collection electrode is grounded.
 7. The electrostatic airsampling device of claim 1, further comprising a transceiveroperationally connected to the electrostatic air sampling device for:controlling the operation of the device in response to received signalsand sending information from the device to a remote location.
 8. Theelectrostatic air sampling device of claim 1, wherein the airborneparticles are selected from: bacterial, fungal, mycoplasma, and moldcells, bacterial, fungal, and mold spores, and prions.
 9. Theelectrostatic air sampling device of claim 1, wherein the potentialapplied to the conical, outer electrode is less than 5,000 volts. 10.The electrostatic air sampling device of claim 1, wherein the powersource additionally provides power to the collection electrode.
 11. Theelectrostatic air sampling device of claim 10, wherein the power sourceis programmed to variably energize the electrode segments of theconical, outer electrode.
 12. The electrostatic air sampling device ofclaim 1, wherein the cylindrical collection electrode is a hollowcylinder having an interior volume and further comprising: a reservoircontaining a liquid, said reservoir hydraulically connected to thecollection electrode and a pump for pumping liquid from the reservoir tothe interior volume of the collection electrode such that liquid flowsfrom the interior of the electrode and over the outer surface of thecollection electrode and is returned to the reservoir.
 13. Theelectrostatic air sampling device of claim 12, wherein the devicecomprises two or more electrostatic collection modules that share acommon reservoir.
 14. The electrostatic air sampling device of claim 12,further comprising an analyzer hydraulically connected to the reservoir,for analyzing particles collected by the sampling device.
 15. Theelectrostatic air sampling device of claim 12, wherein the liquid is anaqueous buffer.
 16. A method for collecting airborne particulatescomprising: drawing air through an electrostatic air sampling devicecomprising: an electrostatic collection module comprising: an airflowchamber comprising an air passage having an air inlet and an air outlet;a means of drawing air into the air inlet, through the airflow chamber,and out through the air outlet; an ionization electrode located near theair inlet, the ionization electrode being capable of ionizing airborneparticles; a conical outer electrode forming at least a part of theouter wall of the airflow chamber and having a larger diameter towardthe air inlet and a smaller diameter toward the air outlet; acylindrical collection electrode, the exterior surface of which forms atleast a part of the inner wall of the airflow chamber and upon whichairborne particles deposit; and a power source operatively connected tothe electrostatic collection module, said power source providing powerto energize the ionization and outer electrodes; and recoveringcollected particles from the collection electrode.
 17. The methodaccording to claim 16, wherein: the conical, outer electrode of theelectrostatic collection module comprises a series of electrode segmentsand the potentials applied to the electrode segments are programmed toincrease the collection efficiency for desired airborne particulates.18. The method according to claim 16, wherein: the cylindricalcollection electrode is a hollow cylinder having an interior volume andthe electrostatic collection module further comprises: a reservoircontaining a liquid, said reservoir hydraulically connected to thecollection electrode and a pump for pumping liquid from the reservoir tothe interior volume of the collection electrode such that liquid flowsfrom the interior of the electrode and over the outer surface of thecollection electrode and is returned to the reservoir and collectedparticles are recovered from the collection electrode by collectingliquid from the reservoir.
 19. The method according to claim 16, whereinthe airborne particles are selected from: bacterial, fungal, mycoplasma,and mold cells, bacterial, fungal, and mold spores, and prions.
 20. Themethod according to claim 16, wherein the air inlet of the airflowchamber comprises one or more vanes that cause tangential, spiral,laminar airflow in the airflow chamber.